There might be life on other planets, but so far scientists haven't found enough ________ to prove it.

When I first set _________ in Germany, I didn’t know what the future might have in _________ for me.

Speaking of what sort of smartness is most desirable in human __________，a friend of mine told me a story.

The young woman rushed to the hospital ________ she heard the terrible news.

Please refer to the   before you switch on the engine.